Relation between NFC antenna size and reading range

PoolBear · ‎2024-03-04

Hi @Brian TIDAL @Rene Lenerve @JL. Lebon

Can you please help me understand how antenna size in st25dv64kc tag effect the reading range and another question is like in iso15693 tag reading range is 60cm but practically working with tag my experience the effective range of communication between tag and nfc enabled phone is 6cm why is this?

JL. Lebon · ‎2024-03-04

Hello,

There are a lot of physical parameters that are involved in read range vs antenna size and that can't be easily develop here without entering deeply into math equations.
But basically, the more magnetic fields "lines" the antenna can capture, the better it is for read range. That means larger antennas provides more read range. But there are some other factors, like coupling factor between the reader antenna and the tag antenna, or reader's antenna size and reader's power.

The 60cm are practically achieved with high power readers with large antenna (for example the FEIG LR1002, that can deliver 4w on a 30cm antenna) and large tag antenna (class 1, credit card size).

A smartphone doesn't deliver enough power to reach such distances and usually have small antenna.
With a ST25DV on a class 1 antenna (credit card size antenna 50x80mm), you can expect 6 to 10cm read range depending on smartphones. If the ST25DV uses a smaller antenna like class 6 (20x25mm), expect between 3cm and 5cm with smartphones.
If you are using a more powerful reader like ST25R3916, you can expect to almost double those figures.

Best regards.

View solution in original post

JL. Lebon · ‎2024-03-04

Hello,

There are a lot of physical parameters that are involved in read range vs antenna size and that can't be easily develop here without entering deeply into math equations.
But basically, the more magnetic fields "lines" the antenna can capture, the better it is for read range. That means larger antennas provides more read range. But there are some other factors, like coupling factor between the reader antenna and the tag antenna, or reader's antenna size and reader's power.

The 60cm are practically achieved with high power readers with large antenna (for example the FEIG LR1002, that can deliver 4w on a 30cm antenna) and large tag antenna (class 1, credit card size).

A smartphone doesn't deliver enough power to reach such distances and usually have small antenna.
With a ST25DV on a class 1 antenna (credit card size antenna 50x80mm), you can expect 6 to 10cm read range depending on smartphones. If the ST25DV uses a smaller antenna like class 6 (20x25mm), expect between 3cm and 5cm with smartphones.
If you are using a more powerful reader like ST25R3916, you can expect to almost double those figures.

Best regards.

PoolBear · ‎2024-03-04

@JL. Lebon for us mobile is always reader and tag is passive device so what is the size of antenna in case of tag we can use for max range according to st

PoolBear · ‎2024-03-04

@JL. Lebon We are actually thinking of designing a customize nfc antenna in a pcb board so if you have any suggestions to get max reading range with a nfc enabled phone pls share

JL. Lebon · ‎2024-03-05

Hello,

The max antenna size will mainly depend on your constraints (size available in your box or on your PCB for example), so only you can tell.
As for recommendation, with smartphones as readers, I think there is no need to go with a tag antenna size larger than class 1 (credit card size antenna 50x80mm). With smartphones, larger antenna will provide any benefit because the phone antenna size are usually smaller than that. From my experience, class 1 provides the best results.

Best regards.

JL. Lebon · ‎2024-03-05

Hello,

To maximize read range, on top of antenna size, it is important that the antenna is correctly tuned. I recommend tuning the antenna to 13.7MHz.
It is also important not to block the field with any metal part or ground plane close to the antenna.

Best regards.

PoolBear · ‎2024-03-06

@JL. Lebon

can you please give me a approx. range for each type of antenna for nfc enabled mobile

class1-6-10cm according to our previous discussion

class2

class3

class4

class5

class6 -3-5cm

can you give me a approx. range for each type

JL. Lebon · ‎2024-03-06

Hello,

I don't have precise figures for all size of antennas. Please keep in mind that all smartphones are different (different antenna size and different power), so the figures are only indicative and approximate.

With a class 1, as said, you can expect 6-10cm.
With a class 3, you can expect 4 to 6cm.
With a class 6, you can expect 3 to 4cm (5cm was a bit optimistic).

For the other antenna size, you are in-between those values with overlapping because of disparity between smartphones.

Best regards.

MrDave · ‎2024-03-08

I have a similar question. The antenna I'm attempting to match is Taoglas FXR.07.52.0075X.A, and I've been scouring AN4974 and the ST25R Antenna Matching Tool. Much of it I have figured out, realize a VNA is critical to success so have a nanoVNA on order for that. EMC Inductor and associated DC Resistance for the EMI filter - Got that. When it gets to the Target Z I'm a bit lost, for Target Q I understand that is just a method of attenuation.

The over all goal is a 30mm-40mm read range.

I guess I could also use some help with the datasheet parameter mapping of the Taoglas antenna into the Antenna parameters section of the Antenna Matching Tool.

-Dave

JL. Lebon · ‎2024-03-12

Hello MrDave,

Please note that AN4974 is an application note for designing antennas for readers, it is not relevant for passive tags where you certainly don't want to add EMC filtering or matching network.
The correct application note for tag antenna design is https://www.st.com/resource/en/application_note/an2972-how-to-design-an-antenna-for-dynamic-nfc-tags-stmicroelectronics.pdf.

Initial question of this message thread was for tag antenna design. Are you designing an antenna for a tag or for a reader? If this is for reader, please open another ticket so that subjects are not mixed.

Best regards.